EXTERNAL CHARACTERS. 11 



pupil appears nearly round, or straight when the 

 snbtriangular form obtains (Fig. 2, a). In some 

 specimens of Bombinator the upper border is even 

 emarginate, so as to produce the shape of a heart ; and 

 when extremely contracted the pupil divides into 

 three branches, affecting the shape of a Y (Fig. 2, a) 

 This type of pupil approaches the vertical, and in 

 some specimens of Discoglossus the much-contracted 

 pupil is in fact a little deeper than broad. In Alytes, 

 Pelodytes, and Pelobates (Fig. 2, b, c) we find a regular 

 cat's pupil, vertically elliptical or club-shaped, linear 

 when fully contracted. 



The tympanum, or drum of the ear, is absent in 

 Bombinator and Pelobates. When present it may be 

 concealed under the skin, as in some specimens of 

 Discoglossus, Pelodytes, and Bufo vulgaris, or appear 

 on the temple behind the eye as a round or oval disk 

 covered with thin skin (Fig. 1, a, p. 9). 



The mouth is large, and cleft to beyond the eyes. 

 The jaws are edentulous in Bufo ; the upper is armed 

 with numerous closely-set teeth in the other genera — 

 ten to fifteen in each prasmaxillary, forty to fifty in 

 each maxillary. The teeth have sharply-pointed, 

 slightly-hooked crowns with long shafts applied to 

 the inner side of the prgemaxillary and maxillary 

 bones. The palate (Fig. 3, p. 12) is pierced by two 

 pairs of orifices, the choanse, or inner openings of the 

 nostrils anteriorly, and the openings of the Eusta- 

 chian or auditory tubes, situated near the commis- 

 sures of the jaws; the Eustachian tubes are extremely 

 fine, or sometimes even indistinct, in Bombinator. In 

 all the genera except Bufo there are two groups or 

 series of teeth, each implanted on an eminence of the 

 vomerine bones ; these vomerine teeth are situated 

 between or behind the choanse, as shown on p. 12, 

 Fig. 3, a, c, d. 



The tongue, thick and papillose, flat, is attached in 

 front and in the middle, and the posterior portion, by 

 being bent over and rapidly thrust out of the mouth, 



